His brain was not much larger than a chimpanzee’s. Yet his widened pelvis implied his kind gave birth to children with much bigger brains.
And so a fossilized adolescent named Karabo — which means “answer” in a South African dialect — is raising a lot of questions about human evolution.
Researchers found his skeleton, and much of an adult female’s, in a cave about 25 miles north of Johannesburg in 2008 and announced the discovery in 2010. They coined a new species, Australopithecus sediba , and launched an intensive multinational effort to study the find.
In the journal Science, the team provides detailed descriptions of the creatures’ heads, hands, feet and hips. It also dates the fossils to 1.98 million years ago, smack in the middle of an era famous for its lack of evidence of possible human relatives.
The mash-up of humanlike and apelike traits resemble a “a stop-action snapshot of evolution in action,” said Richard Potts, director of the Smithsonian Institution’s Human Origins Program. He was not involved in the research.
The researchers stop just short of calling the creatures an ancestor to the human lineage known as Homo. But they place A. sediba squarely in the running for that coveted title.
The species is “possibly the best candidate” yet for a Homo ancestor, said Lee R. Berger of the University of Witwatersrand in Johannesburg. Berger, along with his then-9-year-old son Matthew, discovered Karabo in a fossil-rich region known as the Cradle of Humankind.
Over the past four decades, scientists have sketched in branches on the human evolutionary tree from nearly a dozen species of creatures that roamed East and South Africa stretching back 4 million years. The emerging picture is not a linear march from ape to man but rather a profusion of cousin species overlapping in time and space. Some died out, others continued to evolve — but divining which were which has proved challenging.
The new fossils’ feet and ankles are “mostly human,” said Bernhard Zipfel, also of the University of Witwatersrand. And yet, the heel looks more apelike — one of many such anomalies.
The knee lined up above the ankle, not angled out as in apes, a giveaway that the creatures walked upright. And yet, bumps on the inside of the ankle and other features mark the ankle as more chimplike, the “type of ankle you need to climb a tree,” Zipfel said.
The thumb was long relative to the fingers — even longer than ours. The fingers curved, suggesting a powerful grasp. Toolmaking “was possible,” said Tracy Kivell of the Max Planck Institute for Evolutionary Anthropology in Germany, although the scientists have found no stone tools nearby.
In France, scientists scanned Karabo’s skull using high-powered X-rays. The imprint of the brain on the inner skull suggests that certain areas had begun to evolve and grow into those of more humanlike species, the researchers said.